1. Field of the Invention
The present invention relates to medical instruments such as needle assemblies, and more particularly to depth setting mechanisms for such needle assemblies.
2. Prior Art
A major medical problem exists where about 13 million Americans suffer from kidney and urinary tract-related diseases. Currently, over 200,000 Americans are hospitalized each year for kidney stones. All patients with a renal or upper ureteral calculi requiring surgical removal are candidates for percutaneous ultrasonic liphotripsy, a procedure by which kidney stones are fragmented with ultrasonic energy and extracted through an endoscope. To perform the percutaneous ultrasonic liphotripsy, a needle and thin guide wire are inserted through a skin puncture and are advanced under fluoroscopy through the renal pharemchyma into a middle or lower calix. In some cases the operation is also visualized with ultrasound by itself or in combination with the fluoroscopy. The needle being inserted has to be inserted only to a specific depth. In one form of the prior art, a sterile tape is placed on a teflon-sheet needle at the measured distance from the needle tip. The needle would then be inserted up the tape prior to the subsequent introduction of catheters to facilitate kidney drainage and the like. Needless to say, placing a tape circumferentially above a needle and injecting that needle into a patient could certainly be deleterious to the health of a patient.
A number of different devices have been shown wherein the depth of a needle may be preselected. U.S. Pat. No. 4,356,822 to Winstead-Hall shows an arrangement of locking ribs. The series of ribs engage one another when the plunger is rotated so as to strike thereagainst. This concept however, only allows specific projections of the needle, there is not an infinite number of depth settings available.
U.S. Pat. No. 3,356,089 to Francis shows a long needle joined in the forward end of the medication barrel and generally closely surrounded by a sheath so that the controlled advancing and retracting of the medication barrel a selected distance is permitted.
A further depth setting arrangement is shown in U.S. Pat. No. 2,338,800 to Burke, wherein a locking guide is engagable on the end of a needle. The locking guide comprises a plate which prevents further insertion of the needle into the patient. A further U.S. Pat. No. 4,332,248 to DeVitas has a support guide which provides an aid to inserting a needle into its desired depth. An unusual depth setting device is shown in U.S. Pat. No. 3,538,916 to Wiles which is described as an injection pistol having a proximal end of a shaft which has a threaded means on the end of a shaft which is adjustable to pre-select the depth to which the needle will advance into the patient.
An adapter assembly shown in U.S. Pat. No. 4,187,848 enables a syringe and a catheter to be locked together, to permit a liquid to be pumped through the adapter to the catheter. No suggestion is made of using the adapter as a locking device on a barrel to facilitate depth setting thereof with a sheath.
It is an object of the present invention to overcome the limitations of the prior art.
It is a further object of the present invention to provide a depth setting arrangement for a needle which is self contained and easy to set.
It is still a further object of the present invention to provide a depth setting apparatus which is sterilizable within its own container.